The invention relates to a power factor correction circuit (PFCC), particularly for power supply systems requiring high output power, high efficiency and high power factor. The PFCC converts AC, e.g. line, voltage into DC voltage and can be employed as pre-regulator of a switching power supply.
Power factor well defines performance of a switching power supply. It is a ratio of the output power over input power. The input power is input AC voltage multiplied by RMS input current. The power factor is often specified only for the PFCC. In fact, the power factor depends on efficiency of the entire device.
A conventional switching power supply converts AC energy source, e.g. line, into DC voltage. In particular, the line voltage is rectified and further applied to an input capacitor.
Charging the capacitor causes inrush current and surge currents every peak of the line voltage. Numerous interference suppressors and protection circuits are inevitable. Power factor is very poor.
A conventional PFCC employs boost switching circuit. Rectified line voltage is applied thereto. Switching frequency or pulse width modulation (PWM) varies in a large range. The voltage provided by the boost circuit is inherently greater than peak of the line voltage. The PFCC operates as a separate input unit. In particular, controllable switches of the PFCC must sustain a full output power of the switching power supply. Moreover, the inrush current is inevitable.